1. Field of the Invention
The invention the subject of the present application relates to methods of making tobacco smoke filter elements.
2. Brief Description of the Prior Art
The most widely established method of manufacture of cigarette filter elements comprises the continuous feeding of plasticiser treated cellulose acetate tow and a web of wrapper paper to a garniture unit of a rod making machine. A driven endless band extends through the garniture unit and serves to convey the tow and wrapper paper web through the unit, wherein the wrapper papers is wrapped about the tow and lap seamed, there thereby being continuously produced a rod of circular cross-section. Downstream of the garniture unit the rod is cut into lengths a multiple, commonly six, of a unit element. Subsequent cutting of the rod lengths during the making of filter tipped cigarettes provides discrete filter elements. A similar method is used, although to a lesser extent, for the manufacture of paper filter elements, a web of crimped filter paper rather than cellulose acetate tow being fed to the garniture unit.
There have also been proposed methods of making filter rod by the extrusion of foamed thermoplastics materials. Such proposals have been disclosed in United Kingdom Patent Specification No. 451,683 (Sharman), United Kingdom Patent Specifications Nos. '1,271,274; 1,341,400; 1,442,631; 1,456,908 and 1,482,216 (Monsanto Chemicals Limited or Monsanto Limited) and in U.S. Pat. Specification No. 4,180,536 (Celanese Corporation).
Mention is made in United Kingdom Patent Specification No. 694,436 (Mayer-Neville) of a cigarette filter element formed by rolling into cylindrical form a strip of porous latex foam. Similar filter elements are disclosed in United Kingdom Patent Specification No. 799,781 (Cogepa).
United Kingdom Patent Specifications Nos. 1,122,661 and 1,279,803 (Monsanto Chemicals Limited) relate to cigarette filter elements made from an extruded, foamed thermoplastic material which has been drawn, to impart unidirectional orientation to the material, and then worked in order to break down the foam structure and to produce a three dimensional structure of interconnected fibre elements.
United Kingdom Patent Specification No. 993,602 (Du Pont) teaches a method of making cigarette filter rod wherein a polyoxymethylene is extruded as a foamed structure ribbon, the ribbon is shredded under the action of a wire brush and the shreds are wrapped in a paper web. United Kingdom Patent Specification No. 1,183,498, in the name of the present applicants, teaches the comminution of synthetic foam materials, as for example in a hammer mill, and the wrapping of the resultant particulate material in paper to provide filter rod. A class of foam materials disclosed in United Kingdom Patent Specification No. 1,205,766 (National Patent Development Corporation) is said to provide a suitable tobacco smoke filter medium, especially when the materials are in particulate form. According to United Kingdom Patent Specification No. 1,194,492 (Strickman Foundation), a tobacco smoke filtration material is provided by granulating a rigid polyurethane foam.
It is proposed in U.S. Pat. No. 3,800,808 (Brown & Williamson Tobacco Corporation) to make cigarette filter material by encasing a starch with a cellulose ester, cellulose acetate for example, swelling the starch and then removing the starch by enzymation and/or chemical hydrolysis or by solubilising the starch. The resultant foamed product is cut into shreds, which shreds are used as filter material for filter rod.
Although numerous proposals have been made in the patents literature for the use of foamed materials in or as cigarette filters, these proposals have failed to find practical application in the tobacco industry.
It is an object of the present invention to provide a method of making commercially acceptable filter elements, which method is practical and simple. It is another object of the present invention to provide a method in which readily available and inexpensive materials can be used to make commercially acceptable filter elements.